tcp: Fix a data-race around sysctl_tcp_invalid_ratelimit.

stable inclusion
from stable-v4.19.255
commit 69eab4c78d7a366d75de3d07e0a4a9e7c81291c1
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I5Q0SQ
CVE: NA

--------------------------------

[ Upstream commit 2afdbe7b ]

While reading sysctl_tcp_invalid_ratelimit, it can be changed
concurrently.  Thus, we need to add READ_ONCE() to its reader.

Fixes: 032ee423 ("tcp: helpers to mitigate ACK loops by rate-limiting out-of-window dupacks")
Signed-off-by: NKuniyuki Iwashima <kuniyu@amazon.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>
Signed-off-by: NSasha Levin <sashal@kernel.org>
Signed-off-by: NYongqiang Liu <liuyongqiang13@huawei.com>

net/ipv4/tcp_input.c

@@ -3423,7 +3423,8 @@ static bool __tcp_oow_rate_limited(struct net *net, int mib_idx,
 	if (*last_oow_ack_time) {
 		s32 elapsed = (s32)(tcp_jiffies32 - *last_oow_ack_time);
 
-		if (0 <= elapsed && elapsed < net->ipv4.sysctl_tcp_invalid_ratelimit) {
+		if (0 <= elapsed &&
+		    elapsed < READ_ONCE(net->ipv4.sysctl_tcp_invalid_ratelimit)) {
 			NET_INC_STATS(net, mib_idx);
 			return true;	/* rate-limited: don't send yet! */
 		}